Nearly 1,500 white sturgeon became stranded last week within Port Susan Bay's shallow channels near Stanwood, apparently while searching for food. Almost all survived by swimming back into the depths of Puget Sound after the tide came in several hours later.

All they wanted was a hearty lunch.

Instead, nearly 1,500 white sturgeon found themselves stranded last week within Port Susan Bay’s shallow channels near Stanwood. Almost all survived by swimming back into the depths of Puget Sound after the tide came in several hours later.

Some fish biologists speculate that the sturgeon, some reaching 10 feet long, were hungry for critters found in shallow mud flats. When the tide dropped, the fish were trapped in the estuary’s shallow channels, unable to move across the exposed, muddy ground to deeper water.

Colder water temperatures that day, March 12, also could have made the fish lethargic, biologists said.

“I think these were just fish that were poking around, looking for food,” said Brett Barkdull, a fish biologist with Washington Department of Fish and Wildlife who lives near the stranding area. “These fish have been out here for quite a while now, but I’ve personally never seen anything quite like this.”

He said he spoke with local residents who also had never seen a similar stranding.

Barkdull first visited the site early this week and found about a dozen sturgeon that perished in the stranding. Most of the dead fish were large — 5 to 10 feet long, he said.

Still, white sturgeon are known to be tough and resilient, said Jason Griffith, a fish biologist with the Stillaguamish Tribe. The bottom-dwelling species has been around for more than 100 million years and originate in several West Coast rivers. Most of the white sturgeon in Puget Sound were born in the Fraser and Columbia rivers and migrate to find food.

The colossal, prehistoric-looking fish can live well over 100 years and tip the scales at 400 pounds or more. They grow bony, armorlike plates for protection and feed on shellfish, small fish and worms.

It’s not unusual to find many sturgeon congregating in Port Susan, an area with plenty to eat. Though most of the stranded fish initially survived, some of the larger ones could be affected later because of stress, said Brad James, a Department of Fish and Wildlife biologist.

Compared to salmon, not a lot is known about white sturgeon, James said, and scientists occasionally are baffled by their behavior and habits. For instance, last year biologists found thousands of living sturgeon clumped together at the bottom of the Columbia River below Bonneville Dam, possibly to stay warm.

As for the Puget Sound stranding, scientists may never know for sure why the sturgeon got caught, other than the pursuit of a meal.

“It looks like they chose to overextend their visit on the mud flats,” James said. “The feeding must have been pretty good.”

Michelle Ma: 206-464-2303 or mma@seattletimes.com